A wiring structure formed by a damascene process technique has conventionally been known. For example, in a conventional multilayer wiring structure, a barrier layer (barrier metal) is formed between an interlayer insulating film and Cu (copper) which is a material of a wiring line) to prevent Cu from being diffused into the insulating film. With this wiring structure, since the barrier layer having a predetermined thickness is provided between the insulating film and Cu, wiring may be inevitably delayed due to increased resistance (contact resistance). With regard to this problem, the following Non-Patent Documents 1 and 2 disclose a wiring structure in which no barrier layer is provided between the insulating film and Cu.